The invention relates to a light arrangement for an optical device for measurement of an index of refraction, comprising a light source, a fiber bundle arrangement for transmitting light from the light source, a diffusing member for receiving light from the light source and creating an even light distribution, and optics for receiving light from the diffusing member and for transmitting the light to a measuring window. The invention relates also to a refractometer having a light arrangement and an optical device for measurement of an index of refraction.
This type of light arrangement is known from U.S. Pat. No. 9,632,025 B2. A problem with known light arrangements is that they are prone to braking when they are used for measuring indexes of refraction from hot substances, where the temperature of the substances exceeds 100° C. More specifically, the light source may, owing to overheating, break if the light source is a light emitting diode. If the light source is arranged at a long distance from the prism and its measuring surface to prevent overheating of the light source, the fiber bundle becomes long and prone to breaking owing to impacts and vibration. Also, other electronical components then the light source may break in high temperatures. Another problem with a long fiber bundle arrangement is that its alignment with respect to the prism and its measuring surface is difficult to carry out.